Fault tree method is one of the important analysis methods in project risk assessment which can identify and assess risks in various system and not only finds out the direct reason, it deeply reveals the potential causes of the accident. The cause and effect can be described in an intuitive, clear, straight forward and logical way and both qualitative analysis and quantitative analysis can be made. This paper establishes fault tree model for the Yuetang dam to determine the factor of risk of the dam failure so as to provide reasonable grounds of reinforcing for the managers.